1. Field of the Invention
The field of the invention concerns hearing instruments, and particularly hearing instruments with directional microphones.
2. Description of the Prior Art
Conventional hearing instruments typically comprise a single omni-directional microphone, which amplifies sound substantially equally from all directions. Because of the omni-directional nature of these hearing instruments, it is often difficult for the wearer to distinguish between a speaker's voice and background noise. Hearing instruments have therefore been developed that accentuate a speaker's voice over background noise.
Directional microphones may be implemented in hearing aids in several ways. In one system, two or more omni-directional elements are linked to two or more individual ports. One microphone is linked to each port, and electrical signals are processed in order to extract the directional response. Alternatively, one or more directional elements may be linked to two or more ports. One directional microphone is linked to two ports, and the signal is processed by the directional element. The difference in sound intensity on the closely-positioned ports of this type of directional hearing aids is typically negligible and the information about the direction of arriving sound signals is derived from the phase differences of the sound signals.
However, directional microphones, although suitable for isolating a speaker's voice, typically have signal-to-noise ratios less than that of omni-directional microphones. Also, directional microphones are very sensitive to wind noise. Thus, in environments with little background or high wind noise, an omni-directional microphone is more desirable for use in processing sound. Therefore, hearing instruments have been developed that include both an omni-directional and a directional microphone, wherein a wearer switches between the two modes as desired.
Unfortunately, hearing instruments that contain both an omni-directional microphone and a directional microphone typically have lower sensitivity in the directional mode and are larger in size as compared to hearing instruments containing only an omni-directional microphone. These dual mode hearing instruments generally have two separate microphone cartridges and a separate toggle switch for switching between them. The total space occupied by these components limits their use to users with ears large enough to accommodate the devices. An unfortunate result is that children often cannot make use of these larger devices.
Accordingly, the hearing instrument industry seeks reduced sized hearing instruments with improved sensitivity and simplified assembly, yet having the advantages of both omni-directional and directional functionality.